Foam core article with flexible heat-resistant knitted fabric

ABSTRACT

A foam core article such as a mattress or pillow is covered on a surface with a flexible heat-resistant knitted fabric. Preferably a further sacrificial fabric also is used to allow passage of CPSC 16 CFR 1633 with a peak heat release of no more than 200 kilowatts in a 30 minute time period following ignition.

RELATED APPLICATION

The present patent application is a continuation-in-part of Ser. No. 11/897,581 file Aug. 31, 2007.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention is directed to an article having a foam core such as a mattress or pillow in combination with a flexible heat-resistant knitted fabric. In a preferred embodiment the invention also employs a sacrificial fabric.

2. Description of Related Art

The State of California has led the drive to regulate and reduce the flammability of mattresses and mattress sets in an attempt to reduce the number of lives lost in household, hotel, and institutional fires. In particular, the Bureau of Home Furnishings and Thermal Insulation of the Department of Consumer Affairs of the State of California issued Technical Bulletin 603 “Requirements and Test Procedure for Resistance of a Residential Mattress/Box Spring Set to a Large Open-Flame” to quantify the flammability performance of mattress sets.

A further test procedure to determine the suitability of a mattress construction with a fire barrier is set forth in test procedure CPSC 16 CFR1633.

A mattress normally contains a mattress core covered by cushioning material or batting that is in turn covered with an outer fabric ticking. Most cushioning material or batting is made from foam or fiber materials that will burn when exposed to an open flame. Therefore a substantial effort has been made to cover a mattress with a fire resistant barrier to conform to flammability regulations.

A need is present for an improved fire barrier material and improved construction which retard burning of an article having a foam core.

SUMMARY OF INVENTION

The present invention in a preferred mode is directed to a mattress with a flexible heat-resistant knitted fabric comprising:

(I) a mattress having a foam core and

(II) a flexible heat-resistant knitted fabric covering at least a portion of a surface of the mattress wherein the knitted fabric comprises:

(a) para-aramid yarn; and

(b) cellulosic yarn wherein cellulosic material in the yarn has not been treated to improve fire resistance, with the provisos:

(i) the para-aramid is present in an amount of at least 38 percent by weight of the knitted fabric on a basis of para-aramid and cellulosic material in the yarns,

(ii) the para-aramid yarn has a size in a range from 45 cc to 16 cc,

(iii) the cellulosic yarn has a size in a range from 45 cc to 16 cc and

(iv) the knitted fabric has a stitch density in a range from 300 to 1200 stitches per square inch.

Also the present invention is directed to other articles with a foam core article with an example being a pillow or other furniture cushioning.

In a most preferred embodiment a sacrificial fabric is employed with the foam core article and the flexible heat-resistant knitted fabric.

DETAILED DESCRIPTION OF THE INVENTION

A preferred substrate of the present invention is a mattress having a foam core. Due to the flammability of the foam an added degree of protection is needed to resist burning particularly since a mattress may include more than one layer of foam with different densities, different materials and different degrees of resiliency. The mattress may or may not contain springs for resiliency. In a preferred embodiment, the mattress does not contain springs which conventionally denotes a need for a larger mass of foam.

In the present invention the mattress is at least partially covered on its outer surface (i.e. a surface which faces an observer) with a flexible heat-resistant knitted fabric. The knitted fabric contains para-aramid yarn and cellulosic yarn. The cellulosic material is not treated to impart fire resistance and accordingly does not impart an added degree of fire resistance to the yarn compared to a cellulosic material with, for example, a fire resistant chemical.

The para-aramid is present in an amount of at least 38 percent by weight on a basis of para-aramid and cellulosic material in the knitted fabric. Preferably the para-aramid will be at least 40 percent on this basis. Accordingly the weight ranges are 38 to 60 percent para-aramid and correspondingly 40 to 62 percent cellulosic material. A more preferred range is 40 to 60 percent para-aramid and 40 to 60 percent cellulosic material.

For purposes of the present invention, the following definitions are employed.

As employed herein a foam core denotes a resilient material having gas bubbles entrapped therein

A co-fed yarn is a yarn resulting from more than one yarn being fed into at least one needle of a knitting machine but the action is that of a single yarn forming the course of the fabric. At least two of the yarns being fed into a needle are of different composition.

An alternate yarn arises when only one yarn is fed into a needle of a knitting machine but yarns of different composition are fed into different needles so that the action is that of the courses of the fabric being formed from different yarns.

Plated fabric contains loops composed of two (or more) yarns, usually with differing physical properties. Each has been separately supplied through its own guide or guide hole to the needle hook, in order to influence its respective position relative to the surface (face and back of the fabric).

Knitted fabric denotes a fabric which is knitted with yarns containing para-aramid and yarns containing cellulosic material wherein the yarns are intermixed in the fabric, i.e. the yarns do not lie in separate layers such as one fabric layer containing only para-aramid yarns and another separate layer containing only cellulosic material.

As used herein “cellulosic” and “cellulosic material” includes cotton, rayon and combinations. However this definition is employed to exclude cellulosic materials which have been treated for the purpose imparting flame resistance (FR). According FR cotton and FR rayon are excluded in calculating the above-stated weight percentage requirements.

The knitted fabric containing para-aramid yarns and cellulosic yarns imparts heat resistance such as from a flame (in air) due to an ability to retard burning for a period of time. This resistance is present even though the cellulosic material can readily burn.

However a further criteria for the heat-resistant knitted fabric is an ability to have flexibility and a degree of stretch. Illustratively the heat-resistant knitted fabric typically will cover one surface of a mattress with wrapping of the fabric around corners of the mattress. A preferred use is where the fabric covers all exterior mattress surfaces. The flexibility and stretch of the heat-resistant knitted fabric allows such use.

The flexibility and stretch of the heat-resistant knitted fabric is imparted by use of para-aramid yarn and cellulosic yarn within a specific size range as well as within a specific stitch density range. Both the para-aramid yarn and the cellulosic yarn feedstock will have a size in a range from 45 cc to 16 cc (cc means cotton count in accordance with standard nomenclature). A preferred range for both yarns is 45 cc to 20 cc. Although a single ply yarn is preferred, it is understood that more than one ply may be employed in a yarn. The knitted fabric has a stitch density in a range from 300 to 1200 stitches per square inch (47 to 188 stitches per square centimeter). A preferred range is 450 to 1000 stitches per square inch (70 to 157 stitches per square centimeter).

The weave of the flexible heat-resistant knitted fabric is not critical provided the above criteria are present. Examples of suitable knitted fabrics include jersey (or single) knits, rib (or double) knits, terry knits and French terry knits. A plated knit is a particularly preferred fabric construction.

In a preferred embodiment an article resulting from a mattress and flexible heat-resistant knitted fabric will pass CPSC 16 CFR1633 which is a burning test. Accordingly in conformance with this test a maximum heat peak release is necessary, namely no more than 200 kilowatts in a 30 minute time period following ignition.

In order to pass this test in the present invention a sacrificial fabric is needed in combination with the mattress and flexible heat-resistant knitted fabric wherein the sacrificial fabric faces a heat source employed in the test procedure. The sacrificial fabric denotes a material which burns in the test. The material typically employed is a cotton fabric.

To determine in a mattress and flexible heat-resistant knitted fabric will pass CPCS 16 CFR1633 with a peak heat release of no more than 200 kilowatts in a 30 minute time period, a terry cloth cotton fabric (untreated for fire resistance) is employed on a weight basis of 8 ounces per square yard and use of such fabric is denoted herein as “test procedure A” which is useful for screening purposes. It is understood in actual use by a consumer that another sacrificial fabric and/or another weight may be and would be expected to be used.

Although the above description of the invention is directed to a mattress with a foam core, it is understood that other materials which use a foam core are suitable. An example is a pillow or other furniture cushioning.

To further illustrate the present invention, the following examples are provided. All parts and percentages are by weight unless otherwise indicated.

COMPARATIVE EXAMPLE A

In Comparative Example A, a foam core mattress made from a 8 ounces per square yard terry knit cover fabric comprising cotton and polyester yarns available from A Lava and Sons, Chicago, II, a flame resistant, circular, jersey knit barrier comprising co-fed 18 s/1 cotton yarn available from Parkdale Mills, Gastonia, N.C. and 45 s/1 Kevlar yarn available from Charles Craft, Inc., Laurinburg, N.C. (equivalent to a 29% Kevlar, 71% cotton blend of yarns), and a foam core comprising a 3 inch visco-elastic polyurethane foam layer and a 7 inch dense polyurethane foam layer available from Leggett and Platt, Inc., Chicago, Ill. were collected. The foam core mattress was produced by inserting the foam core into the flame resistant, circular, jersey knit barrier, each end of the jersey knit tube was sewn closed with 60 Tex Kevlar thread available from Coats and Clark, Charlotte, N.C., and finally inserting the flame resistant, jersey knit covered foam core into the terry knit cover fabric. The foam core mattress was then tested for overall mattress flammability per CPSC standard 16 CFR 1633. The foam core mattress had the following results: Two out of three foam core mattress sets failed the CPSC 16 CFR 1633 flammability standard by measuring a peak heat release rate of greater than 200 kW in the first 30 minutes after ignition. See Table 1.

COMPARATIVE EXAMPLE B

In Comparative Example B, a small scale foam core mock up was made from a 8 ounces per square yard terry knit cover fabric comprising cotton and polyester yarns available from Tempur-Pedic International, Lexington, Ky., a 3.9 ounces per square yard flame resistant, circular, 22 cut jersey knit barrier comprising alternately fed 20/1 cotton count cotton yarn available from American House Spinning, Central, S.C. and 20/1 cotton count Kevlar® yarn available from Charles Craft, Inc., Laurinburg, N.C. (equivalent to a 50% Kevlar®, 50% cotton blend of yarns), and a 3 inch thick high density polyurethane foam block available from Hickory Springs Manufacturing Co., Hickory, N.C. The foam core mock up was produced by covering the foam block with the flame resistant, jersey knit barrier, pinning edges of the jersey knit to the back side of the foam with straight pins, and finally covering the flame resistant, jersey knit covered foam block with the terry knit cover fabric, likewise securing it with straight pins on the foam block back side. The flame resistant, jersey knit was either fully relaxed or stretched 30 percent by pulling the barrier across the foam in length and width directions and measuring the percent increase in length times width of an indicated square originally measuring 5 inches on a side. The small scale foam core mock up was then secured vertically in a steel test frame and exposed to the flame of a side surface burner set up as specified by CPSC standard 16 CFR 1633 in which propane gas flow to the burner was 6.6 liters per minute, the flame exposure period was 50 seconds, and the burner was located 1.69 inches from the covered surface of the mock up. Mass loss over time was recorded for three samples each of relaxed and 30 percent stretched knit barriers, and mass loss rate constants were calculated. The higher the relative mass loss rate constant, the lower is the thermal performance of the knit barrier. For this example, the thermal performance of the stretched knit fabric was about 30 percent worse than the thermal performance of the unstretched knit fabric. The results are shown in Table 2.

EXAMPLE 1

In Example 1, a foam core mattress made from a 8 ounces per square yard terry knit cover fabric comprising cotton and polyester yarns available from A Lava and Sons, Chicago, II, a flame resistant, circular, jersey knit barrier comprising co-fed 30 s/1 cotton yarn available from Parkdale Mills, Gastonia, N.C. and 30 s/1 Kevlar yarn available from Charles Craft, Inc., Laurinburg, N.C. (equivalent to a 50% Kevlar, 50% cotton blend of yarns), and a foam core comprising a visco-elastic polyurethane foam layer and a dense polyurethane foam layer available from Leggett and Platt, Inc., Chicago, Ill. were collected. The foam core mattress was produced by inserting the foam core into the flame resistant, circular, jersey knit barrier, each end of the jersey knit tube was sewn closed with 60 Tex Kevlar thread available from Coats and Clark, Charlotte, N.C., and finally inserting the flame resistant, jersey knit covered foam core into the terry knit cover fabric. The foam core mattress was then tested for overall mattress flammability per CPSC standard 16 CFR 1633. The foam core mattress had the following results: three foam core mattress sets passed the 16 CFR 1633 test requirements that included a heat release rate of no more than 200 kW in the first 30 minutes after ignition and a total heat release of no more than 15 MJ in the first 10 minutes after ignition. See Table 1.

EXAMPLE 2

In Example 1, a foam core mattress made from a 8 ounces per square yard terry knit cover fabric comprising cotton and polyester yarns available from A Lava and Sons, Chicago, Ill., a flame resistant, circular, jersey knit barrier comprising co-fed 30 s/1 cotton yarn available from Parkdale Mills, Gastonia, N.C. and 45 s/1 Kevlar yarn available from Charles Craft, Inc., Laurinburg, N.C. (equivalent to a 40% Kevlar, 60% cotton blend of yarns), and a foam core comprising a visco-elastic polyurethane foam layer and a dense polyurethane foam layer available from Leggett and Platt, Inc., Chicago, Ill. were collected. The foam core mattress was produced by inserting the foam core into the flame resistant, circular, jersey knit barrier, each end of the jersey knit tube was sewn closed with 60 Tex Kevlar thread available from Coats and Clark, Charlotte, N.C., and finally inserting the flame resistant, jersey knit covered foam core into the terry knit cover fabric. The foam core mattress was then tested for overall mattress flammability per CPSC standard 16 CFR 1633. The foam core mattress had the following results: two foam core mattress sets passed the 16 CFR 1633 test requirements that included a heat release rate of no more than 200 kW in the first 30 minutes after ignition and a total heat release of no more than 15 MJ in the first 10 minutes after ignition. The one sample failure was caused by the incorporation of a head to toe seam in the flame resistant, jersey knit barrier. This seam was included for the express purpose of creating a flame resistant, jersey tube for full scale mattress testing. This seam will not be apart of the proposed final product and thus this blend of Kevlar® and cotton fiber is considered to pass the CPSC standard 16 CFR 1633. See Table 1.

EXAMPLE 3

In Example 3, a small scale foam core mock up was made from a 8 ounces per square yard terry knit cover fabric comprising cotton and polyester yarns available from Tempur-Pedic International, Lexington, Ky., a 4.0 ounces per square yard flame resistant, circular, 22 cut jersey knit barrier comprising plated 30/1 cotton count cotton yarn available from American House Spinning, Central, S.C. and 45/1 cotton count Kevlar® yarn available from Charles Craft, Inc., Laurinburg, N.C. (equivalent to a 40% Kevlar®, 60% cotton blend of yarns), and a 3 inch thick high density polyurethane foam block available from Hickory Springs Manufacturing Co., Hickory, N.C. The foam core mock up was produced by covering the foam block with the flame resistant, jersey knit barrier, pinning edges of the jersey knit to the back side of the foam with straight pins, and finally covering the flame resistant, jersey knit covered foam block with the terry knit cover fabric, likewise securing it with straight pins on the foam block back side. The flame resistant, jersey knit was either fully relaxed or stretched 30 percent by pulling the barrier across the foam in length and width directions and measuring the percent increase in length times width of an indicated square originally measuring 5 inches on a side. The small scale foam core mock up was then secured vertically in a steel test frame and exposed to the flame of a side surface burner set up as specified by CPSC standard 16 CFR 1633 in which propane gas flow to the burner was 6.6 liters per minute, the flame exposure period was 50 seconds, and the burner was located 1.69 inches from the covered surface of the mock up. Mass loss over time was recorded for three samples each of relaxed and 30 percent stretched knit barriers, and mass loss rate constants were calculated. The higher the relative mass loss rate constant, the lower is the thermal performance of the knit barrier. For this example, the thermal performance of the stretched knit fabric was about 17 percent better than the thermal performance of the unstretched knit fabric. The results are shown in Table 2.

EXAMPLE 4

In Example 4, a small scale foam core mock up was made from a 8 ounces per square yard terry knit cover fabric comprising cotton and polyester yarns available from Tempur-Pedic International, Lexington, Ky., a 4.2 ounces per square yard flame resistant, circular, 10 cut jersey knit barrier comprising co-fed 20/1 cotton count cotton yarn available from American House Spinning, Central, S.C. and 20/1 cotton count Kevlar® yarn available from Charles Craft, Inc., Laurinburg, N.C. (equivalent to a 50% Kevlar®, 50% cotton blend of yarns), and a 3 inch thick high density polyurethane foam block available from Hickory Springs Manufacturing Co., Hickory, N.C. The foam core mock up was produced by covering the foam block with the flame resistant, jersey knit barrier, pinning edges of the jersey knit to the back side of the foam with straight pins, and finally covering the flame resistant, jersey knit covered foam block with the terry knit cover fabric, likewise securing it with straight pins on the foam block back side. The flame resistant, jersey knit was either fully relaxed or stretched 30 percent by pulling the barrier across the foam in length and width directions and measuring the percent increase in length times width of an indicated square originally measuring 5 inches on a side. The small scale foam core mock up was then secured vertically in a steel test frame and exposed to the flame of a side surface burner set up as specified by CPSC standard 16 CFR 1633 in which propane gas flow to the burner was 6.6 liters per minute, the flame exposure period was 50 seconds, and the burner was located 1.69 inches from the covered surface of the mock up. Mass loss over time was recorded for three samples each of relaxed and 30 percent stretched knit barriers, and mass loss rate constants were calculated. The higher the relative mass loss rate constant, the lower is the thermal performance of the knit barrier. For this example, the thermal performance of the stretched knit fabric was about 22 percent better than the thermal performance of the unstretched knit fabric. The results are shown in Table 2.

TABLE 1 FR Mattress CPSC 16 CFR 1633 Test Results Comparative Example A Example 1 Example 2 Barrier Co-fed 29% Kevlar, Co-fed 50% Kevlar, Co-fed 40% Kevlar, 71% Cotton circular, 50% Cotton circular, 60% Cotton circular, jersey knit jersey knit jersey knit Foam Core Visco-elastic foam top Visco-elastic foam top Visco-elastic foam top Construction with polyurethane with polyurethane with polyurethane foam base foam base foam base Cover Fabric Knit 60% Cotton, 40% 60% Cotton, 40% 60% Cotton, 40% Composition polyester polyester polyester Peak HRR (kW) in 178.1* 39.8 42.9 30 min 40.9 39.7 256.6** 539 41.6 99.8 Total Heat Release 8.4* 12.1 5.9 (MJ) in 10 min 6.7 10.4 17.5** 9.9 5.3 10.7 *Test stopped for safety reasons due to samples imminent failure. **Test failed due to a seam in the barrier incorporated for purpose of testing. This head to toe seam is not intended to be apart of the final mattress construction.

TABLE 2 Mass Loss Rate Constants for Unstretched vs. 30% Stretched Flame- Resistant Knit Barriers of Different Knit Constructions Comparative Example B Example 3 Example 4 Knit 22 cut 3.9 osy 22 cut 4.0 osy 10 cut 4.2 osy Description 20 cc/1 Kevlar ® 45 cc/1 Kevlar ® 20 cc/1 Kevlar ® &20 cc/1 cotton &30 cc/1 cotton &20 cc/1 cotton alternately fed plated yarns co-fed yarns yarns Unstretched 0.030 0.047 0.037 Knit Mass Loss Rate Constant (g{circumflex over ( )}0.5/s) 30% Stretched 0.039 0.039 0.029 Knit Mass Loss Rate Constant (g{circumflex over ( )}0.5/s) 

1. An article of a mattress with a flexible heat-resistant knitted fabric comprising: (I) a mattress having a foam core; and (II) a flexible heat-resistant knitted fabric covering at least a portion of a surface of the mattress wherein the knitted fabric comprises: (a) para-aramid yarn; and (b) cellulosic yarn wherein cellulosic material in the yarn has not been treated to improve fire resistance, with the provisos: (i) the para-aramid is present in an amount of at least 38 percent by weight of the knitted fabric on a basis of para-aramid and cellulosic material in the yarns, (ii) the para-aramid yarn has a size in a range from 45 cc to 16 cc, (iii) the cellulosic yarn has a size in a range from 45 cc to 16 cc and (iv) the knitted fabric has a stitch density in a range from 300 to 1200 stitches per square inch.
 2. The article of claim 1 wherein, the mattress does not contain springs.
 3. The article of claim 1 wherein, the para-aramid is poly(paraphenylene terepthalamide).
 4. The article of claim 1 wherein, the cellulosic material is cotton or rayon.
 5. The article of claim 4 wherein, the celullosic material is cotton.
 6. The article of claim 1 wherein, the para-aramid yarn has a size in a range from 40 cc to 20 cc and the cellulosic yarn has a size in a range from 40 cc to 20 cc and the knitted fabric has a stitch density in a range from 450 to 1000 stitches per square inch.
 7. The article of claim 1 wherein the knitted fabric is a plated knit.
 8. The article of claim 1, which additionally contains a sacrificial fabric with a construction in order (a) mattress, (b) flexible heat-resistant knitted fabric and (c) sacrificial fabric, wherein, the article passes CPSC 16 CFR1633 with a peak heat release of no more than 200 kilowatts in a 30 minute time period after ignition.
 9. The article of claim 8 wherein, the sacrificial fabric comprises cotton.
 10. An article comprising in order: (I) a foam core, (II) a flexible heat-resistant knitted fabric covering at least a portion of a surface of the foam core wherein the knitted fabric comprises (a) para-aramid yarn and (b) cellulosic yarn wherein cellulosic material in the yarn has not been treated to improve fire resistance, with the provisos: (i) the para-aramid is present in an amount of at least 38 percent by weight of the knitted fabric on a basis of para-aramid and cellulosic material in the yarns, (ii) the para-aramid yarn has a size in a range from 45 cc to 16 cc, (iii) the cellulosic yarn has a size in a range from 45 cc to 16 cc and (iv) the knitted fabric has a stitch density in a range from 300 to 1200 stitches per square inch and (III) a sacrificial fabric, with the proviso the article passes CPSC 16 CFR1633 with a peak heat release of no more than 200 kilowatts in a 30 minute time period after ignition.
 11. The article of claim 8 having a CPSC16 CFR1633 thermal performance after stretching the knit fabric by 30 percent of at least 10 percent higher than the thermal performance of a similar article in which the knit fabric is not stretched.
 12. The article of claim 10 wherein, the sacrificial fabric comprises cotton.
 13. A method for making a knitted fabric of claim 1 comprising the step of feeding the aramid and cellulosic yarns so that the aramid and cellulosic yarns lie on separate sides of the fabric 